As an update to the earlier version published in 2021, this policy brief outlines the blue carbon ecosystems that are currently ‘actionable’ for climate mitigation, based on the best available science and existing management practices. Additionally, this policy brief identifies the ecosystems that are ‘emerging’ and may become actionable in the future (macroalgae, benthic sediments and mudflats), as well as ecosystems that do not currently have a mitigation pathway but offer other critical benefits for climate adaptation and resilience, biodiversity, and livelihoods (such as coral reefs, oyster reefs and marine fauna). This brief does not consider climate mitigation options that move ecosystems further from their natural state and have possible negative impacts on human health and wellbeing, such as kelp afforestation and ocean fertilization. Non-ecosystem-based options for ocean carbon dioxide removal (CDR) are also not considered in this brief.